The demand in recent years for further increases in the capacity of displays in areas such as image quality and screen size has lead to the development of a range of displays collectively referred to as flat panel displays (FPDs). Representative FPDs include liquid crystal displays (LCDs) and plasma display panels (PDPs).
LCDs are formed from a backlight mounted to the rear of a liquid crystal panel and a color filter mounted on a front surface of the liquid crystal panel, the panel becoming transparent when electricity is supplied. The widespread usage of LCDs in personal computers, televisions, and the like, is anticipated.
PDPs, on the other hand, are generally formed from two thin glass substrates on which are arranged a plurality of electrodes and dielectric films (or dielectric layers). The two glass substrates are arranged to face each other with a plurality of barrier ribs (hereafter “ribs”) interposed between, and phosphor layers are arranged in the gap (“rib gap”) between adjacent ribs. A space between the two glass substrates is filled with a discharge gas, and the substrates are sealed together such that the space therebetween is airtight. A phosphor illumination results from a discharge generated in the discharge gas when electricity is supplied. Unlike cathode-ray tube (CRT) displays, increases in PDP screen size result in only minimal increases in the depth and weight of the display unit, and PDPs are additionally noted for their unlimited viewing angle.
The current demand for increases in the screen size and image quality (resolution) of FPDs such as these has resulted in the availability on the market of PDPs having a screen size in excess of 50 inches.
However, moves are now being made to further increase the capacity of high resolution PDPs. For instance, current demands require high-vision PDPs to have 1920×1125 pixels, a 0.14 mm×0.45 mm cell pitch, and a per cell surface area of approximately 0.063 mm2. A PDP realizing such a capacity would exhibit a much higher resolution than NTSC compatible PDPs currently in use. In order to achieve such a capacity it is necessary for the phosphor layers to be formed as minutely as they are for high-vision displays (i.e. a rib pitch in the order of 0.1 mm to 0.15 mm).
Unexamined patent application publication 10-192541 filed in Japan discloses an inkjet (linejet) method for this purpose, which allows phosphor ink to be discharged from a fine nozzle and applied in rib gaps between adjacent ribs.
FIG. 3 is a front cross-sectional view of a nozzle unit 800 and an ink tank 900 used in the disclosed inkjet method. Nozzle unit 800 is a hollow rectangular parallelepiped formed from SUS steel and includes a lid 801, a housing 802, and a soleplate 803.
Soleplate 803 is perforated with a plurality of nozzle holes 700 formed at a regular pitch (e.g. the pitch of the phosphor layers corresponding to any one of the colors red, green, and blue). A perforated valve opening V3 in lid 801 is connected via an Si tube L1 to a valve opening V2 in ink tank 900 which stores the phosphor ink. Compressed air supplied at a regular pressure (e.g. 4˜5 kg/cm2) through a valve opening V1 in the top of ink tank 900 forces the phosphor ink to run into nozzle unit 800, from where the ink is discharged from the plurality of nozzle holes 700.
However, as shown in FIG. 4A, discharging the phosphor ink according to the disclosed inkjet method often results in the ink flows from nozzle holes 700 reacting with each other due to electrostatic action, causing some of the ink flows to warp and thus preventing the vertically downward flow of the ink. Consequently, application of the ink on a target surface is impeded, and phosphor layers are formed in which the colors may be mixed and incorrect amounts of ink may be applied to given surface areas. The result is uneven brightness across the range of cells.
As seen above, there exists room for improvements in stability and accuracy with respect to methods for applying phosphor ink through an ink nozzle.
Moreover, problems of erroneous application due to electrostatic action can arise and need to be resolved with respect to not only phosphor ink but all the various types of ink applied in the formation of the layers of LCDs, PDPs, and other FPDs.
In view of the above issues, an object of the present invention is to provide an ink for a display panel, such as a phosphor ink, that can be applied efficiently and with precision. A further object of the present invention is to provide a method for manufacturing high quality plasma display panels using the ink.